Aluminum alkyls are well known as cocatalysts for conventional Ziegler Natta catalysts. More recently, many new catalysts for olefin polymerization have been invented. These new catalysts are, in general, well defined organometallic compounds with bulky ligands (whereas, in contrast, the prior art Ziegler Natta catalysts are, in general, simple transition metal halides). Numerous cocatalysts or activators have been proposed for these new catalysts, including methyl aluminoxane (or “MAO”) and ionic boron activators. These cocatalysts/activators provide high activity but are expensive to synthesize.
An elegant family of alkoxy aluminates are disclosed In U.S. Pat. No. 5,895,771 (Epstein et al.) but the data reported in this patent illustrate that these aluminates are not particularly active.
We have now discovered a simple chelating borate which provides excellent activity for olefin polymerization.